1. Field of the Invention
The present invention relates to a printing device capable of automatically distinguishing rank characteristic of a print head mounted in the printing device.
2. Description of the Related Art
There has been known a conventional ink jet printing device that includes piezoelectric elements. The piezoelectric elements deform upon application of voltage. This mechanical deformation of the piezoelectric elements can be used to eject ink droplets for printing. However, a great deal of variation can be seen in manufactured piezoelectric elements. Therefore, even when driven using the same voltage, different heads will eject ink droplets with volumes and at speeds that vary between different print heads. Because different print heads require different voltages, it is necessary to investigate characteristics of the heads before mounting the print heads on printing devices. Print heads are divided into a plurality of ranks according to voltage required to drive them.
One printing device is provided with a control unit for automatically distinguishing the rank of the print head mounted therein and then setting the voltage to be applied to the print head according to the determined rank of the print head. Before the print head is mounted in the print device, circuits provided to the print head unit are cut in a pattern according to the rank characteristic. When the print head is mounted in the print device, the control unit distinguishes the rank of the print head by using a digital signal that varies depending on how the circuits are cut.
Circuitry used by the control unit of this conventional printing device will be described while referring to FIGS. 14 and 15. FIG. 14 is a circuit diagram of the circuit for distinguishing head rank. FIG. 15 is a block diagram of the control system in the printing device provided with the circuit shown in FIG. 14.
As shown in FIG. 14, in the conventional circuit for designating print head rank, a signal line 116 connecting a ground (0 V) and a central process unit (CPU) 150 is divided into two signal lines 122, 124. A cut unit 110 is disposed on a chip mounting board (not shown in FIG. 14) and includes a cut portion 112 for cutting the signal line 122 and a cut portion 114 for cutting the signal line 124. A resistor unit 120 is disposed on the chip mounting board (not shown in FIG. 14) and includes a resister R4 connected to the signal line 122 and a resister R5 connected to the signal line 124. The signal lines 122 and 124 are connected to output their signals to separate predetermined ports of the CPU 150.
When assembling the driver IC chip 160 into the ink jet recording device, the cut portions 112 and 114 are cut in a manner depending on the rank of the print head, that is, depending on the required drive voltage to be set. Three possible cut patterns are possible, that is, when one or the other of the cut portions 112 and 114 are cut and when neither are cut. According to the cut pattern, one of three digital signals 01, 10, or 00 is outputted across the signal lines 122, 124 to the CPU 150. After determining the type of digital signal, the CPU 150 retrieves a drive voltage corresponding to the determined digital signal from a table stored in a RAM, for example, of the recording device.